US3763919A - Method of making a mold - Google Patents

Abstract

The moulding material comprises porous iron blocks distributed around the mold cavity and sand containing a binder whose binding action is destructable by heat. The surface of the mold cavity is substantially wholly sand. The mold cavity is bounded by a layer of the sand supported by a backing of porous iron blocks.

Description

United States Patent 11 1 11 3,763,919 Sundin Oct. 9, 1973 [54] METHOD OF MAKING A MOLD FOREIGN PATENTS OR APPLICATIONS 1 lnvemofl Per 5 Sundin, Jonkoping, 879,354 10/1961 Great Britain 164/23 Swe en [73] Assignee: Hoganas AB, Hoganas, Sweden Primary Examiner.l. Spencer Overholser Assistant Examiner-John E. Roethel [22] Flled' 1971 Attorney-Holman & Stern [21] Appl. No.: 201,440

[57] ABSTRACT if 5' 164/22 164/ 1 2; The moulding material comprises porous iron blocks d 22 distributed around the mold cavity and sand contain- 1 e o are l ing a binder whose binding action is destructable by heat. The surface of the mold cavity is substantially 1 1. :12:in?:1lgzntzig t bitzrg sfi 3130: 112:

UNITED STATES PATENTS blocks 2,940,140 6/1960 Frantz 164/24 X 3,273,211 9/1966 Miraldi 164/24 6 Clams 2 Drawmg Flgures METHOD OF MAKING A MOLD BACKGROUND OF THE INVENTION This invention relates to the casting of metals, in particular iron and steel, in sand molds.

In many known types of molds, a mold cavity is defined by a molding material consisting mainly of sand. The sand is usually moist and therefore conducts heat away from the molten metal too quickly for there to be a uniform cooling rate throughout the casting. When the casting is removed the sand remains as a bound mass and cannot usually be reused without further processing. Another disadvantage of the known molds is the large quantity of sand required, which generally excludes the use of expensive sands which would give better castings.

SUMMARY OF THE INVENTION The present invention provides a method of making a mold, including forming against a pattern in a molding box a molding material comprising porous iron bodies and sand containing a binder whose binding action is destructable by heat, the surface adjacent the pattern being substantially wholly sand.

It is to be understood that the unqualified term iron" includes carbon steel and low-alloy steel.

The porous iron bodies absorb moisture from the layer of sand so that the surface of the mold cavity has a low heat conductivity. Also after molten metal has been poured into the mold, the binding action of the binder is at least partially destroyed, so that the unbound sand and porous iron bodies can be recovered after removal of the casting.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described further, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a vertical longitudinal section through a mold; and

FIG. 2 is a vertical section through part of another mold, as it is formed on a pattern.

DETAILED DESCRIPTION OF THE DRAWING FIG. I shows a mold contained in an upper mold box 1 and a lower mold box 2. The mold has an upper part 3, a lower part 4 and a core 5. All these parts are made from sand 9 containing a' heat-decomposable binder and porous iron blocks 6, preferably made from sponge iron. The molding cavity 7 is bordered by surfaces which are formed wholly by the sand 9, and the porous iron blocks 6 are embedded in the sand.

One-tenth to one-half of the volume of the molding material consists of sand, and the rest of the volume is occupied by the porous iron blocks 6. The layer of sand between the molding cavity 7 and the blocks 6 may be thin, i.e. have a thickness between I and 300 mm. Heavy castings (i.e. with a weight of 50 tons or more) normally require a layer thickness exceeding 100 mm. while a layer thickness of l to 20 mm is usually sufficient for small castings. The main purpose of the sand is to bound the mold cavity and to form a cement between the porous iron blocks which constitute the body of the mold and the core.

A gate 8 is formed in the upper part of the mold. Because of the firmness of the mold and the slow and even solidification of the cast metal, the need for feeding more molten metal into the mold during solidification is decreased, which means that the gate can be made relatively small, as shown in FIG. I.

The amount of binder is preferably between I and 5 percent of the total amount of sand. I

The binder used in the sand can be a suitable heatdecomposable organic substance, such as furan or a cellulose derivative for example. As a consequence of the accumulation of heat due to the low thermal conductivity of the dry sand, the temperature of the sand is raised to such a high level during casting that the binder is almost completely decomposed, which in turn makes it possible to reclaim the sand in a simple fashion by passing it through a screen equipped with a cyclone for dust separation. This leads to a substantially decreased sand consumption. In addition the amount of sand for each mold is reduced to between 1/10 and V2 of the amount used in a conventional mold, depending on the shape of the casting. As a consequence of the low sand consumption it becomes feasible to use the same type of sand for the mold as for the core.

It has been mentioned above that the sand can be reclaimed in a simple way. In addition the porous iron blocks 6 can of course be recovered and used again, the number of times being practically unlimited. The consumption of molding material is therefore minimal.

A near percent utilization of the sand in the mold itself is achieved if the upper as well as the lower part of the mold are made in such a manner that the porous iron blocks are shaped to conform to the desired casting and so as to leave only a thin space into which the sand can be blown. The thickness of the layer of sand which thus becomes attached to the porous iron blocks (which suitably can be pre-heated to the setting temperature of the binder mixed with the sand) should be chosen with consideration of the weight and dimensions of the casting, as mentioned above.

This is illustrated in FIG. 2, which shows a mold con structed from shaped blocks 10 of porous iron forming a backing kept together by a molding box or frame 11 with a layer of sand 13 (containing furan as a binder) in the space between the porous iron blocks 10 and a pattern 15. The gate 14 is also used for introducing the sand. This mould is particularly suitable for mass production of relatively light castings, e.g. motorcar engines, machine stands, and the like, i.e. castings weighing up to a couple of tons.

Since the porous blocks absorb water from the binder as it sets, the mold becomes firm and insulating, which makes the cast metal solidify very evenly practially regardless of whether the wall thickness of the casting is large or small. This in turn leads to a hardly measurable difference in structure and hardness between the surface and the center of the casting.

In the types of mold described above, the surface which bounds the mold cavity is wholly formed by sand. The porous iron blocks, which have a capacity for absorbing liquid (especially water) and have a relatively high thermal conductivity, are preferably made from sponge iron, but other forms such as compressed turnings or the like can also be used.

Since the mold described above are good thermal insulators it becomes possible to cast the metal at a lower temperature than hitherto, which of course is an economic advantage.

The molds described above provide for reduced sand consumption in the mold, partly by increasing the amount of sand reclaimed and partly by decreasing the amount of sand used in making each mold. Because of the low sand consumption more expensive sand such as chromite, zircon, or olivine sand can come into wider use for molding, whereas the use of these sands has been on a very limited scale up to now. When these kinds of sand are used, health hazards due to silicosis are reduced or even eliminated.

I claim:

1. A method of making a mold for the casting of metal, comprising the steps of a. arranging a plurality of water-absorbent porous iron blocks in a molding box around a pattern so as to be adjacent to but not in contact with the pattern and so as to fill substantially the whole of the space around the pattern in the molding box;

b. filling the space between the blocks and the pattern with sand containing a binder which sets on warming and whose binding action is destroyed on heating to a predetermined temperature;

0. setting the binder; and

d. removing the pattern to leave a continuous layer of sand of substantially uniform thickness supported by a backing of porous iron blocks;

whereby, when molten metal is cast into the mold, any water in the sand evaporates and is absorbed by the porous iron blocks to leave a heat-insulating layer of dry sand to ensure slow and even cooling of the casting, and the binding action of the binder is destroyed by heating so that the sand and porous iron blocks can be easily recovered.

2. A method as claimed in claim 1, further comprising the step, before filling said space with sand, of heating the porous iron blocks to a temperature at which said binder will set.

3. A method as claimed in claim 1, in which said sand is selected from the group consisting of chromatic sand, zircon sand, and olivine sand.

4. A method as claimed in claim 1, in which the binder makes up between 1 percent to 5 percent by weight of the total amount of sand.

5. A method as claimed in claim 1, in which the binder is selected from the group consisting of furan and cellulose derivatives.

6. A method as claimed in claim 1, in which the porous iron blocks are sponge iron.

Claims (6)

1. A method of making a mold for the casting of metal, comprising the steps of a. arranging a plurality of water-absorbent porous iron blocks in a molding box around a pattern so as to be adjacent to but not in contact with the Pattern and so as to fill substantially the whole of the space around the pattern in the molding box; b. filling the space between the blocks and the pattern with sand containing a binder which sets on warming and whose binding action is destroyed on heating to a predetermined temperature; c. setting the binder; and d. removing the pattern to leave a continuous layer of sand of substantially uniform thickness supported by a backing of porous iron blocks; whereby, when molten metal is cast into the mold, any water in the sand evaporates and is absorbed by the porous iron blocks to leave a heat-insulating layer of dry sand to ensure slow and even cooling of the casting, and the binding action of the binder is destroyed by heating so that the sand and porous iron blocks can be easily recovered.

2. A method as claimed in claim 1, further comprising the step, before filling said space with sand, of heating the porous iron blocks to a temperature at which said binder will set.

3. A method as claimed in claim 1, in which said sand is selected from the group consisting of chromatic sand, zircon sand, and olivine sand.

4. A method as claimed in claim 1, in which the binder makes up between 1 percent to 5 percent by weight of the total amount of sand.

5. A method as claimed in claim 1, in which the binder is selected from the group consisting of furan and cellulose derivatives.

6. A method as claimed in claim 1, in which the porous iron blocks are sponge iron.

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